According to TTC website, it designates the model and can be seen on ***THIS*** page fourth from the bottom.

Looks like a heavy duty model and says good for 450 torque. This has the identical gearing as my T-56, so will have the SAME 5th gear as the T-45/T-3650/T-5 transmissions. NO gap between the current 4th~5th you have now, so a much nicer trans for 50~60 MPH cruising.